Why writing JavaScript applications in TypeScript

JavaScript is the language of the Web. There is no other language that can run literally on any old or new device connected to the Internet. On the other hand, there are dozens of languages that compile (a.k.a. transpile) to JavaScript. Why not just writing JavaScript applications in JavaScript? Let me start with analogy with Assembly.

Programs written in a particular flavor of Assembly language run on any device that have a CPU that understand it. See the shortcoming comparing to JavaScript? An Assembly program can’t run on any device, but on any device with a specific CPU architecture. Still, why not writing all the code for a specific platform in Assembly? Why use Java, C#, Python or C++?

We want to be productive. Vast majority of the programmers want to be as far as possible from the bare bone metal. Let compilers and virtual machines convert our programs to the machine code.

We want to be productive in writing JavaScript as well.

Compilers convert the source code into a byte code or a machine code. Transpilers convert a source code of a program in one language into a source code in another one.

You can think of any programming language (other than a machine code) as a syntactic sugar added on top of a another language. While compilers just dissolve all this sugar, transpilers dissolve only a part of it.

Last year I was experimenting with the Dart language. It has a nice syntax (easy for Java and C# developers), which transpiles to to JavaScript. I like Dart, but it requires a special browser with a VM during development. The other negatives are that Dart code transpiles into a difficult to read JavaScript and doesn’t offer easy interoperability with JavaScript frameworks that coexist with the Dart code in most of the applications.

TypeScript was designed by Anders Hejlsberg who also created C#, Delphi, and Turbo C++. TypeScript is a superset of JavaScript, which means that simply renaming existing .js into a .ts file will make it a valid JavaScript code. This is almost always the case except the cases described in this blog.

The TypeScript compiler tsc is actually a transpiler that generates easy to read JavaScript. TypeScript can be compiled into the ES#, ES5, or ES6 flavor of JavaScript, which is a simple option on the command line. You can run tsc in a so called watch mode, so it watches your files for changes and automatically compiles them as soon as you save the file.

Currently I use TypeScript for writing code that uses two frameworks by Google: Angular 2 (it’s written in TypeScript as well) and Polymer.

These are some reasons for writing JavaScript code in TypeScript:

* TypeScript supports types. This allows the TypeScript compiler help developers in finding and fixing lots of errors during development before even running the app.

* Creators of TypeScript follow the ECMAScript 6 standard,and TypeScript 1.6 already supports more than a half of the ES6 syntax. Also TypeScript enriches ES6 by adding types, interfaces, decorators, class member variables (fields), generics, and the keywords, public and private (well, private is not what some might think). See the roadmap of TypeScript.

* TypeScript interfaces allow to declare custom types that will be used in your application. Interfaces help in preventing errors caused by using the objects of wrong types in your application. This feature will be dear to the hearts of Java and C# developers although TypeScript interfaces can be use not only with the implements keyword, but used for presenting object types in a special way.

* The ability to have great IDE support is one of the main advantages that TypeScript has to offer. IDEs as well as some text editors offer great context-sensitive help. The code refactoring of TypeScript is done by IDEs whereas with JavaScript it has to be done manually.

* There is a library DefinitelyTyped that includes hundreds of type definitions files for TypeScript and allows IDEs to perform type checking and offer context-sensitive help while using APIs of literally all JavaScript frameworks.

* The generated JavaScript code is easy to read and looks as a hand-written code. Even though you can generate so called source maps that allow you to debug the TypeScript code inside the browser, you can easily read generated JavaScript and find the corresponding lines in your TypeScript program.

* TypeScript comes with a separate static code analyzer, and several IDEs or text editors already use it (e.g. WebStorm, Atom, Sublime Text, Visual Studio Code, Visual Studio 2015 et al.)

Anyway, today TypeScript is my language of choice for writing the source code for Web browsers. I’m planning to write a couple of more blogs introducing TypeScript syntax. If you want to play with TypeScript, visit http://www.typescriptlang.org.

If you’re a Java developer who kept postponing learning JavaScript till better times, the time is now. You can ease into the JavaScript world via the door marked “TypeScript”.

If you’re planning to work with Angular 2 and want to see how to use TypeScript with this framework, our upcoming “Angular 2 Development with TypeScript” book may come handy.


5 thoughts on “Why writing JavaScript applications in TypeScript

  1. Yakov, thanks for such a helpful blog! Could you share your opinion about ReactJs? As It seems a new way to build ui part of web applications effectively.

    1. Didn’t have a chance to work with React. But TypeScript 1.6 supports the JSX format used in React.

      Regarding UI, I really like Google Polymer web components. You can use them right out of the box, but what’s more important, you can extend them to create app-specific components.

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